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In inorganic chemistry, a bicarbonate (IUPAC-recommended nomenclature: hydrogencarbonate) is an intermediate form in the deprotonation of carbonic acid.
The bicarbonate ion (hydrogen carbonate) is an anion with the empirical formula HCO<sub>3</sub><sup>−</sup> and a molecular mass of 61.01 daltons; it consists of one central carbon atom surrounded by three identical oxygen atoms in a trigonal planar arrangement, with a hydrogen atom attached to one of the oxygens. The bicarbonate ion carries a negative one formal charge and is the conjugate base of carbonic acid, H<sub>2</sub>CO<sub>3</sub>; it is the conjugate acid of CO<sub>3</sub><sup>2−</sup>, the carbonate ion as shown by these equilibrium reactions.
CO<sub>3</sub><sup>2-</sup> +2 H<sub>2</sub>O ⇋ HCO<sub>3</sub><sup>1-</sup> + H<sub>2</sub>O + OH<sup>1-</sup> ⇋ H<sub>2</sub>CO<sub>3</sub> +2 OH<sup>1-</sup>
H<sub>2</sub>CO<sub>3</sub> +2 H<sub>2</sub>O ⇋ HCO<sub>3</sub><sup>1-</sup> + H<sub>3</sub>O<sup>1+</sup> + H<sub>2</sub>O ⇋ CO<sub>3</sub><sup>2-</sup> +2 H<sub>3</sub>O<sup>1+</sup>
A bicarbonate salt forms when a positively charged ion attaches to the negatively charged oxygen atoms of the ion, forming an ionic compound. Many bicarbonates are soluble in water at standard temperature and pressure, particularly sodium bicarbonate and magnesium bicarbonate; both of these substances contribute to total dissolved solids, a common parameter for assessing water quality.
The most common salt of the bicarbonate ion is sodium bicarbonate, NaHCO<sub>3</sub>, which is used as baking soda. When exposed to an acid such as acetic acid (vinegar), bicarbonates release carbon dioxide. This is used to cause bread to rise in baking and to propel toy rockets.
The bicarbonate/carbonate ionic system is also a buffer in blood.
This chemical is also found in the blood. It is a crucial component of the acid/base system of the body (maintaining homeostasis). 86%-90% of CO<sub>2</sub> in the body is converted into H<sub>2</sub>CO<sub>3</sub>, a diprotic acid, which also can turn into its basic form HCO<sub>3</sub><sup>−</sup>. When close to equal amounts of Carbonate ions and Carbonic acid are present it forms a buffer system. This helps maintain the pH of the blood at a level needed for tissues and enzymes to work adequately.
The flow of bicarbonate ions from rocks weathered by the carbonic acid in rainwater is an important part of the carbon cycle.
Bicarbonate also serves a use in the digestive system. It neutralizes the exceedingly acidic pH of the stomach after the stomach digests the food.